Ceramic tiles and natural stones are both beautiful and practical as surface coverings on floors and walls. They may be waterproof, easily cleaned, durable and can be decorated with an infinite variety of colors and designs. Recently they have become quite popular for use in bathrooms, kitchens and foyers where water is frequently present.
House construction commonly calls for wood to be used as subfloors and drywall to be installed on walls. If wood or drywall is repeatedly exposed to water, it swells as it soaks up water, then contracts as the water evaporates. These repeated cycles of expansion and contraction breaks down the cell walls, causing the substrate to soften, decay and disintegrate over time. When wet, these substrates may also be susceptible to attack by molds, causing additional damage.
If finish surface materials such as ceramic tiles and natural stones are applied directly to wood or drywall, cycles of swelling and drying, and the resultant damage, cause problems with cracking and breaking of the finish surface. Ceramic tiles and natural stones are very rigid and brittle materials, and do not give or stretch when the substrate deflects or moves. When the substrate deflects or moves, the attached tile moves with it causing the tile to crack or break when adjacent areas of substrate move. If a cracked or broken tile is not replaced immediately, water will be able to seep through the crack, causing even more swelling and drying of the substrate, resulting further damage to the ceramic tiles.
Typically, 5/16″ or ½″ cement board, such as DUROCK® Brand Cement Board manufactured by USG Corporation, Chicago, Ill., is used under ceramic tile to provide a compatible surface for bonding to the adhesive tile and to provide an underlayment that does not move laterally. If exposed to water, cement does not swell or degrade and it adds strength and stability under the tiles.
However, the use of cement board has certain disadvantages. A half inch thick cement board weighs about 3 pounds per square foot, and can cause fatigue in those who move it to or around the job site or while placing it in position to receive the ceramic tile. Fastening of the cement board to the subfloor requires a large number of fasteners that add extra labor to the cost of the job. Frequently, the board is cut to fit the underlayment at the edges or to go around corners or cabinets. During and after cutting, alkaline fibers in the dust and exposed edges can be irritating to skin or lungs. Cement board is not waterproof and allows transmission of liquids through it. Thus, attempts have been made in the prior art to find an underlayment that is a good adhesive surface, does not move, yet is lighter in weight and less irritating than cement board.
Plastic sheeting has been used as an underlayment for ceramic tiles. It is thin, lightweight and provides a waterproof barrier. However, plastic has a poor surface for bonding of the mortar used to adhere the tiles.
Thin layers of a lightweight, waterproof concrete composition were used to make concrete canoes by engineering students at several universities for a contest in 2003. The University of Alabama at Huntsville team used a mixture of Portland cement, a latex, an acrylic fortifier, plastic microspheres and water. This mixture produced a composition that had good workability and water resistance. It had a weight of only 14.7 pounds per cubic foot.
U.S. Pat. No. 6,455,615 to Yu discloses a flexible polymer modified cement that can be used alone or on a substrate. It is disclosed for use in concealed areas of construction engineering, water conservancy projects and municipal works. A hydraulic cement, a polymer dispersion and water are calendared to form sheets, then dried until the composition is firm. The hydraulic material optionally includes from 20% to about 50% other hydraulic materials, including fly ash, silica fume, metakaolin and slag.